RESUMO
Three Sicilian wastewater treatment plants were monitored to assess the occurrence and the behaviour of radionuclides. Two sampling campaigns (screening and long-term) were carried out during which liquid and solid samples have been analysed. It was found that ¹³¹I mostly occurred in the samples analysed during the screening campaign (43% of the analysed samples contained ¹³¹I). High ¹³¹I specific activity was found in the mixed liquor, recycled sludge and dehydrated sludge samples. This finding was mainly due to the tendency of (131)I to be associated with solid particles. During the long-term sampling campaign an influence of the sludge retention time (SRT) on the ¹³¹I behaviour was found. Increasing the SRT and consequently decreasing the fraction of active organic biomass inside the system, the specific activity of ¹³¹I decreases.